This invention relates generally to methods of cooling an induction-type electrodynamic system such as an electrical generator or motor and, more particularly, relates to a method for improving the heat transfer in stator coil cooling tubes.
In the art, stator coils of an inner-cooled electrodynamic power generator are typically constructed of columns or stacks of copper strands surrounding stacks of cooling tubes through which a coolant such as hydrogen gas or air is circulated. The circulated coolant is used as a means to regulate the temperature of the electrodynamic machine thereby allowing the machine to operate under increased load conditions. While current stator construction is effective in achieving the desired cooling effect, it has been seen that hot-spot temperatures sometime approach the maximum allowable temperature for the particular electrodynamic machine which in turn diminishes the power density of the machine. This hot-spot temperature is especially seen at the end of the stator coil in air cooled machines due to the build up of heat in the coolant gas, and at the end of the embedded length in the core due to higher cross-slot eddy current losses in the hydrogen cooled machines which is typical for their higher power rating. Therefore, a need exists for further minimizing hot-spot temperatures within the stator coils whereby higher power densities in gas cooled electrodynamic machines may be achieved.
As a result of this existing need, it is an object of the present invention to provide an inner cooled coil having improved heat transfer between the walls of the cooling tubes and the gas flowing therein for removing the effect of localized hot-spots.